1. Field of the Invention
The present invention is related to a data transfer system having a transfer discrimination circuit. The system according to the present invention is applicable to a usual or common computer system having a central part at a central location and input/output devices (I/O devices) at remote locations.
2. Description of Related Art
In general, there are two kinds of data transfer used for the channel interface to a computer, i.e., a interlock data transfer in which a maximum transfer speed of 1.5 megabytes per second is attained for a distance of about 5 to 10 m between the input/output channel device and the input/output device (I/O device), and a data streaming feature (DSF) data transfer in which a maximum transfer speed of 3 megabytes per second is attained for a distance of about 120 m between the input/output channel device and the I/O device. In the procedure for the signals in the channel interface, there are no rules prescribed by the computer manufacturer for the signal or the procedure which indicates which of these two kinds of data transfer is being used.
Where an arrangement is used for extending the distance between the input/output channel device and the I/O device, it is necessary to discriminate which data transfer, the interlock data transfer or the DSF data transfer, is being carried out, to realize a satisfactory data transfer.
In general, the interface procedure of the input/output channel device is the same for either of these data transfers, and the data transfer is satisfactorily carried out by the input/output channel device without concern for by which data transfer, the interlock data transfer or the DSF data transfer, the data transfer is being carried out.
However, where the channel interface distance is increased by insertion of a serially connected transmission line, a distance extension device must be provided in the channel interface without disturbing the usual operation of the channel interface.
Therefore, to coincide the operation of the distance extension device with the I/O device, a problem arises in that it is necessary to discriminate by which data transfer, the interlock data transfer or the DSF data transfer, the data transfer is being carried out.